add python 3.9 to setup classifiers (#15208)

Author: kristapratico

sdk/formrecognizer/azure-ai-formrecognizer/setup.py

@@ -68,6 +68,7 @@
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9',
         'License :: OSI Approved :: MIT License',
     ],
     zip_safe=False,